<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="../vue.2.5.1.js"></script>
</head>

<body>
    <div id="watch-example">
        <p>
            watch,是指一种监听，watch是对象，里面有键值对，每个key就是被监听对象，后面的函数式由此触发的行为。
            <input v-model="question">
        </p>
        <p>{{ answer }}</p>
    </div>
    <div id="sky">
        <div>
            <input type="text" v-model='firstName'>
        </div>
        <div>
            <input type="text" v-model='lastName'>
        </div>
        <div>
            {{fullName}}
        </div>
    </div>
</body>
<script>
    // 1.如果一个数据依赖于其他数据，那么把这个数据设计为computed的
    // 2.如果你需要在某个数据变化时做一些事情，使用watch来观察这个数据变化【比如基于变化执行一个网页的打开，computed就做不到】

    //很多时候，watch的代码看起来更繁复，不如computed简洁

    var app = new Vue({
        el: "#sky",
        data: {
            firstName: 'foo',
            lastName: "bar",
            fullName: 'foo bar'
        },
        watch: {
            firstName: function(val) {
                this.fullName = val + ' ' + this.lastName;
            },
            lastName: function(val) {
                this.fullName = this.firstName + " " + val
            }
        }
    });
    var watchExampleVM = new Vue({
        el: '#watch-example',
        data: {
            question: '',
            answer: 'I cannot give you an answer until you ask a question!'
        },
        watch: {
            // 如果 `question` 发生改变，这个函数就会运行
            question: function(newQuestion, oldQuestion) {
                // alert(1);
                this.answer = 'Waiting for you to stop typing...'
                this.debouncedGetAnswer()
            }
        },
        created: function() {
            // `_.debounce` 是一个通过 Lodash 限制操作频率的函数。
            // 在这个例子中，我们希望限制访问 yesno.wtf/api 的频率
            // AJAX 请求直到用户输入完毕才会发出。想要了解更多关于
            // `_.debounce` 函数 (及其近亲 `_.throttle`) 的知识，
            // 请参考：https://lodash.com/docs#debounce
            this.debouncedGetAnswer = _.debounce(this.getAnswer, 500)
        },
        methods: {
            getAnswer: function() {
                if (this.question.indexOf('?') === -1) {
                    this.answer = 'Questions usually contain a question mark. ;-)'
                    return
                }
                this.answer = 'Thinking...'
                var vm = this
                axios.get('https://yesno.wtf/api')
                    .then(function(response) {
                        vm.answer = _.capitalize(response.data.answer)
                    })
                    .catch(function(error) {
                        vm.answer = 'Error! Could not reach the API. ' + error
                    })
            }
        }
    })
</script>

</html>